The present invention relates to a hardcoat for a highly transparent plastic substrate, having good suitability for printing. More particularly, the present invention relates to a hardcoat which has a surface capable of realizing high-speed printing and, in addition, possessing excellent scratch resistance and, at the same time, possesses excellent crack preventive properties, adhesion, and capability of preventing influence of, for example, the deformation of a plastic substrate from extending to the hardcoat, a hardcoat for holograms, a hardcoat film, an antireflection film, and a production process thereof.
The present invention further relates to a hardcoat provided on a highly transparent plastic substrate film, a hardcoat film, and a production process thereof, and more particularly to a hardcoat possessing excellent scratch resistance and, at the same time, excellent crack preventive properties, adhesion, and capability of preventing influence of, for example, the deformation of a plastic substrate from extending to the hardcoat, a hardcoat film, and a production process thereof. The present invention further relates to an antireflection film comprising an antireflection layer provided on the hardcoat. The present invention further relates to a heat reflecting film comprising a heat reflecting layer provided on the hardcoat. The present invention further relates to an ultraviolet shielding film comprising an ultraviolet shielding layer provided on the hardcoat.
In recent years, plastic products are being substituted for glass products from the viewpoints of moldability and a reduction in weight. Since, however, the surface of the plastic products is likely to be scratched, a hardcoat film is in many cases applied to the plastic products to impart scratch resistance. Also in the case of the conventional glass products, there is a growing tendency for a plastic film to be applied thereto to prevent scattering. Due to unsatisfactory hardness of the plastic films, however, a hardcoat is in most cases formed on the surface of the plastic films.
The conventional hardcoat film has been produced by coating the surface of a plastic substrate film with a highly scratch-resistant resin, generally a thermosetting resin or an ionizing radiation curing resin, such as an ultraviolet curing resin, either directly or through an about 1 xcexcm-thick primer layer to a small thickness of about 3 to 15 xcexcm (for example, Japanese Patent Laid-Open No. 151914/1995).
Further, in the conventional hardcoat films, an attempt has been made to add an inorganic filler to a film-forming organic component having a polymerizable functional group to enhance the hardness (for example, Japanese Patent Laid-Open No. 41362/1990).
The conventional hardcoats, however, have a small coating thickness and, hence, hardcoat is directly influenced by the deformation of the plastic substrate film underlying the hardcoat. That is, the surface strength is low and unsatisfactory.
On the other hand, merely increasing the thickness of the hardcoat to a larger value than the conventional thickness, that is, more than 3 to 15 xcexcm, can improve the surface hardness of the hardcoat film, but on the other hand, cracking or peeling is likely to occur and, at the same time, curling derived from cure shrinkage is increased. Therefore, the hardcoat film cannot be put to practical use.
In the conventional hardcoat films, incorporation of the inorganic filler into the organic component having a polymerizable functional group can provide a film having improved surface hardness. In this case, however, cracking and peeling are likely to occur and, at the same time, curling derived from cure shrinkage is increased. This renders the hardcoat film unsatisfactory for practical use.
When the hardcoats are used as protective films for preventing specific products from being scratched, production numbers, dates and the like associated with the product are printed on the hardcoats. In this case, for hardcoats to which scratch resistance has been imparted, for example, by forming a dense film as the surface layer or by imparting slipperiness to the surface, a printing ink is less likely to be penetrated thereinto or a dye for sublimation transfer is less likely to be fixed. This results in poor productivity.
When a tacky layer is present on the backside of the plastic substrate film, the formation of a hardcoat on the other side of the substrate film followed by superposition or winding of the assemblies poses a problem that the tacky layer is transferred to the hardcoat.
When the hardcoats are used as protective films for preventing specific products from being scratched, production numbers, dates and the like associated with the product are printed on the hardcoats. In this case, for hardcoats to which scratch resistance has been imparted, for example, by forming a dense film as the surface layer or by imparting slipperiness to the surface, a printing ink is less likely to be penetrated thereinto or a dye for sublimation transfer is less likely to be fixed. This results in poor productivity.
Accordingly, it is an object of the first invention to solve the above problems involved in hardcoat films using a plastic substrate and to provide a hardcoat for a plastic substrate, a hardcoat for a hologram, a hardcoat film comprising the hardcoat applied to a plastic substrate, an antireflection film comprising an antireflection layer applied onto the hardcoat, and a process for forming a hardcoat which can realize satisfactory hardness properties while enjoying good suitability for printing even in the case of a small coating thickness, can prevent the influence of the deformation of the plastic substrate on the hardcoat, can prevent cracking and peeling of the hardcoat, can bring the pencil hardness of the surface of the hardcoat film to H to 5H, and, further, even when a tacky layer is present on the backside of the plastic substrate with a hardcoat formed on the front side thereof, can prevent the transfer of the backside layer onto the hardcoat. Thus, according to the first invention, there is provided a hardcoat for a plastic substrate, characterized by being produced from a coating component containing one or more organic components having a polymerizable functional group and an inorganic filler, at least one of the organic components being free from a hydrogen bond-forming group.
Further, according to the present invention, there is provided a process for producing a hardcoat for a plastic substrate, characterized by comprising the steps of: coating the surface of a plastic substrate with a coating liquid comprising one or more organic components having a polymerizable functional group and an inorganic filler, at least one of the organic components being free from any hydrogen bond-forming group; drying the coating to remove the solvent in the coating; aging the dried coating at a temperature of 20 to 100xc2x0 C. for 5 sec to 5 min; and then curing the coating.
In the hardcoat film of the present invention comprising a hardcoat applied onto a plastic substrate film, hardness properties have been imparted, for example, by coating the hardcoat either directly or through other layer onto at least one side of the plastic substrate.
According to the hardcoat for a plastic substrate film of the present invention, the content of the inorganic filler in the surface of the hardcoat is larger than that in the interior of the hardcoat, and the surface of the hardcoat has irregularities. This increases the surface area, or a porous structure is present in a very small region. Therefore, the suitability for printing can be enhanced, and the hardcoat is highly non-tacky.
According to the hardcoat for a plastic substrate film of the present invention, reticular connection of at least a part of the inorganic filler is preferred from the viewpoints of preventing cracking and peeling of the hardcoat, preventing curling of the hardcoat film per se, and, at the same time, enhancing the pencil hardness of the hardcoat film in its surface.
Further, according to the hardcoat for a plastic substrate film of the present invention, the formation of an independent network of at least a part of the organic component and the inorganic filler is preferred from the viewpoints of preventing cracking and peeling of the hardcoat, preventing curling of the hardcoat film per se and, at the same time, enhancing the pencil hardness of the hardcoat film in its surface. More preferably, when both at least a part of the network of the organic component and at least a part of the network of the inorganic filler are present independently, the above effects can be further enhanced.
In this case, the hardcoat of the present invention has been produced from one or more organic components having a polymerizable functional group and an inorganic filler, at least one of the organic components being free from a hydrogen bond-forming group. Therefore, the network of the organic component obtained by polymerization of the organic component and the network of the inorganic filler formed by cohesive force between inorganic filler particles themselves can be present independently to some extent while partial entanglement of these networks with each other. This structure can offer a combination of high hardness and high flexibility of the coating. Specifically, the hardcoat film comprising the hardcoat of the present invention applied onto a plastic substrate film, despite high pencil hardness of the surface thereof, can prevent cracking and peeling of the hardcoat and prevent curling of the hardcoat film per se.
If a large number of hydroxyl, carboxyl, amido and other hydrogen bond-forming groups are present in the organic component of the hard coat for a plastic substrate film, the surface of the inorganic filler particles and the organic component are strongly bonded to each other through a hydrogen bond, resulting in breaking of the network structure of the inorganic filler particles per se. This is likely to create such a structure in the hardcoat that inorganic filler particles locally cohere. In this case, the formed film has improved surface hardness, but on the other hand, cracking and peeling are likely to occur and, at the same time, curling derived from cure shrinkage is increased. This renders the hardcoat film unsatisfactory for practical use. For this reason, at least one of the one or more organic components should not have any hydrogen bond-forming group.
The antireflection film of the present invention is characterized by comprising a plastic substrate film, the hardcoat provided either directly or through other layer on the plastic substrate film, and an antireflection layer provided on the hardcoat.
The hardcoat for a hologram label according to the present invention is applied to a hologram label characterized by comprising: a plastic substrate film; provided on one side of the plastic substrate film in the following order, a hologram image-forming layer, an aluminum deposit, and a pressure-sensitive adhesive layer; and the hardcoat provided on the other side of the plastic substrate film.
The hardcoat for a hologram label according to the present invention is characterized in that, in the formation of the hardcoat on one side of a plastic substrate film followed by the formation of a hologram image-forming layer, an aluminum deposit, and a pressure-sensitive adhesive layer in that order on the backside of the substrate film to produce a hologram label, even though the assemblies are put on top of each other or one another or wound in the course of the production of the hologram label, the transfer of a tacky layer, such as a hologram image-forming layer, provided on the backside of the substrate film onto the hardcoat provided on the other side of the substrate film can be prevented.
In this case, the hardcoat of the present invention has been produced from one or more organic components having a polymerizable functional group and an inorganic filler, at least one of the organic components being free from a hydrogen bond-forming group. Therefore, the network of the organic component obtained by polymerization of the organic component and the network of the inorganic filler formed by cohesive force between inorganic filler particles themselves can be present independently to some extent while there is partial entanglement of these networks with each other. This structure can offer a combination of high hardness and high flexibility of the coating. Specifically, the hardcoat film comprising the hardcoat of the present invention applied onto a plastic substrate film, despite high pencil hardness of the surface thereof, can prevent cracking and peeling of the hardcoat and prevent curling of the hardcoat film per se.
Combined use of two inorganic fillers having different primary particle diameters in the formation of the hardcoat to prevent the creation of the tackiness is not limited to the hologram, and is generally applicable to the cases where a tacky layer is present on the backside of the plastic substrate.
It is an object of the second invention to solve the above problems involved in hardcoat films using a plastic substrate and to provide a hardcoat for a plastic substrate film, a hardcoat film comprising the hardcoat applied to a plastic substrate, and a process for forming a hardcoat which can prevent the influence of the deformation of the plastic substrate on the hardcoat, can prevent cracking and peeling of the hardcoat, can prevent curling of the hardcoat film per se, and can bring the pencil hardness of the surface of the hardcoat film to 2H to 5H. It is another object of the present invention to provide an antireflection film, with hardness properties being imparted thereto, comprising an antireflection layer formed on the hardcoat, to provide a heat reflecting film, with hardness properties being imparted thereto, comprising a heat reflecting layer formed on the hardcoat, and to provide an ultraviolet shielding layer, with hardness properties being imparted thereto, comprising an ultraviolet shielding layer formed on the hardcoat.
The above objects can be attained by the following invention. Specifically, according to the second invention, there is provided a hardcoat for a plastic substrate, produced from a coating component containing one or more organic components having a polymerizable functional group and an inorganic filler, at least one of the organic components being free from a hydrogen bond-forming group, at least a part of the inorganic filler having a polymerizable functional group.
According to the present invention, there is further provided a process for forming a hardcoat for a plastic substrate, comprising the steps of: coating the surface of a plastic substrate with a coating liquid comprising one or more organic components having a polymerizable functional group and an inorganic filler, at least one of the organic components being free from any hydrogen bond-forming group, at least a part of the inorganic filler having a polymerizable functional group; drying the coating to remove the solvent in the coating; aging the dried coating at a temperature of 25 to 100xc2x0 C. for 5 sec to 5 min; and then curing the coating.
In the hardcoat film of the present invention comprising a hardcoat applied onto a plastic substrate, hardness properties have been imparted, for example, by coating the hardcoat onto at least one side of the plastic substrate.
According to the hardcoat for a plastic substrate of the present invention, reticular connection of at least a part of the inorganic filler is preferred from the viewpoints of preventing cracking and peeling of the hardcoat, preventing curling of the hardcoat film per se, and, at the same time, enhancing the pencil hardness of the hardcoat film in its surface.
Further, according to the hardcoat for a plastic substrate of the present invention, the formation of an independent network of at least a part of the organic component and the inorganic filler while forming a covalent bond between a part of the polymerizable functional group in the organic component and a part of the polymerizable functional group in the inorganic filler can offer filling effect of the inorganic filler and can prevent cracking and peeling of the hardcoat, can prevent curling of the hardcoat film per se, and, at the same time, can enhance the pencil hardness of the hardcoat film in its surface. Preferably, when both at least a part of the network of the organic component and at least a part of the network of the inorganic filler are present independently while forming a covalent bond between at least a part of the polymerizable functional group in the network of the organic component and at least a part of the polymerizable functional group in the network of the inorganic filler, both the networks reinforce each other, further enhancing the above effect.
More specifically, the hardcoat of the present invention has been produced from one or more organic components having a polymerizable functional group and an inorganic filler, at least one of the organic components being free from a hydrogen bond-forming group. Therefore, the network of the organic component obtained by polymerization of the organic component and the network of the inorganic filler formed by cohesive force between inorganic filler particles themselves can be present independently to some extent while partial entanglement of these networks with each other due to the covalent bond between the polymerizable functional group in at least a part of the inorganic filler and the network of the organic component. This structure can offer a combination of high hardness and high flexibility of the coating, and thus contributes to a significant improvement in coating strength. Specifically, the hardcoat film comprising the hardcoat of the present invention applied onto a plastic substrate film, despite high pencil hardness of the surface thereof, can prevent cracking and peeling of the hardcoat and prevent curling of the hardcoat film per se.
If a large number of hydroxyl, carboxyl, amido and other hydrogen bond-forming groups are present in the organic component of the hard coat for a plastic substrate film, the surface of the inorganic filler particles and the organic component are strongly bonded to each other through a hydrogen bond, resulting in breaking of the network structure of the inorganic filler particles per se. This is likely to create such a structure in the hardcoat that inorganic filler particles locally cohere. In this case, the formed film has improved surface hardness, but on the other hand, cracking and peeling are likely to occur and, at the same time, curling derived from cure shrinkage is increased. This renders the hardcoat film unsatisfactory for practical use. For this reason, at least one of the one or more organic components should not have any hydrogen bond-forming group.
According to the first invention, preferred inorganic fillers have a particle diameter of 0.1 to 0.3 xcexcm. An inorganic filler in the above particle diameter range does not inhibit the motion of the segment of polymer chains, is likely to independently form a network and, even when a large amount of the inorganic filler is present on the outermost surface of the coating, is not detrimental to the transparency of the coating. When the particle diameter is less than 0.01 xcexcm, the formation of an independent network is disadvantageously difficult, while a particle diameter exceeding 0.3 xcexcm is unfavorably detrimental to the transparency.
Regarding the type of the inorganic filler, ultrafine particles of a metal oxide are preferred because they form a strong reticular network in the coating due to strong cohesive force derived from the large surface area. Ultrafine particles of metal oxides usable herein include ultrafine particles of silica, alumina, titania, zirconia, tin oxide, and ITO. The inorganic filler is dispersed in the matrix resin, and, when the content of the inorganic filler is in a given content range, the inorganic filler can reticularly cohere, leading to the formation of a reticular structure through percolation.
According to the present invention, the one or more organic components are preferably such that at least one of the organic components is an ionizing radiation curing resin material having 4 moles or more, per molecule, of a polymerizable functional group which, upon exposure, for example, to heat or ultraviolet light or an electron beam, is polymerized to form a three-dimensionally reticular network. In this case, if hydroxyl, carboxyl, amido and other hydrogen bond-forming groups are present in the organic component, the surface of the ultrafine particles of the metal oxide and the organic component are strongly bonded to each other through a hydrogen bond, resulting in breaking of the network structure of the particles per se. This is likely to create such a structure in the hardcoat that particles locally cohere. In this case, the formed hardcoat lacks in flexibility. For this reason, preferably, at least one of the one or more organic components does not have any hydrogen bond-forming group.
The molecular weight of the organic component used in the present invention is preferably 1000 to 30000 in terms of the number average molecular weight. When the molecular weight is less than 1000, a strong network cannot be formed. On the other hand, when the molecular weight is more than 30000, this excessively large molecular weight unfavorably inhibits the formation of the network of the inorganic filler.
Specific examples of preferred organic components having a polymerizable functional group and free from a hydrogen bond-forming group usable in the present invention include polyfunctional acrylates, such as dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, and urethane (meth)acrylate, epoxy (meth)acrylate, polyester acrylate, polyacryl acrylate, and other oligomers or polymers having 4 moles or more, per molecule, of a polymerizable functional group.
According to the present invention, the weight ratio of the organic component to the inorganic filler is preferably 2:8 to 7:3, particularly preferably 3:7 to 6:4. In the conventional hardcoat, the content of the inorganic filler therein is about 3:7 in terms of the ratio of the inorganic filler to the organic component. On the other hand, according to the present invention, use of one or more organic components, at least one of the organic components being free from a hydrogen bond-forming group and having a polymerizable functional group, have enabled the amount of the inorganic filler added to be increased to a value much larger than that used in the conventional hardcoat. Therefore, the amount of the inorganic filler, present on the outermost surface, necessary for improving the suitability for printing can be increased, and, at the same time, the formation of the network structure of the inorganic filler can be facilitated.
When the amount of the inorganic filler is excessively large, the hardcoat becomes very brittle although the hardness of the coating is increased. On the other hand, when the amount of the organic component is excessively large, the hardness of the coating is extremely lowered.
The ratio of the organic component to the inorganic filler falling within the above range is important for rendering the content of the inorganic filler in the hardcoat larger in the surface of the hardcoat than the interior of the hardcoat to form a surface having irregularities.
The plastic substrate and other layer, which are effective in the hardcoat film according to the present invention, have a pencil hardness of about 4B to HB. An example of this type of plastic substrate is a polyethylene terephthalate film, and an example of this type of other layers is a recording layer or a hologram layer into which information can be written by a laser beam or the like. In applying the hardcoat film onto an object, when the surface of the object in the assembly should be visible, the plastic substrate should be transparent. The pencil hardness of the hardcoat per se is H to 5H.
According to the present invention, xe2x80x9cpencil hardness of the hardcoat per sexe2x80x9d is a pencil hardness as measured, by the pencil hardness test according to JIS K 5400, for a coat formed by coating of the material onto a not less than 25 xcexcm-thick polyethylene terephthalate film to a thickness of about 3 xcexcm on a dry basis. In the pencil hardness test, the test is repeated five times for each of pencils having different hardnesses to determine the hardness of the pencil which, in the repetition of the test five times, did not cause any abnormal phenomenon in the appearance, such as a scratch. For example, in the repetition of the test five times using a pencil of 3H, when any abnormal phenomenon did not occur in the appearance, the pencil hardness of the material is at least 3H.
According to the present invention, xe2x80x9cpencil hardness of the hardcoat filmxe2x80x9d refers to a pencil hardness, as measured by the pencil hardness test according to JIS K 5400, for hardcoat films comprising the hardcoat formed on various plastic substrate films, and is evaluated in the same manner as described above in connection with the xe2x80x9cpencil hardness of the hardcoat per se.xe2x80x9d In this connection, it should be noted that the pencil hardness of the hardcoat film is influenced by the material of the hardcoat, the thickness of the hardcoat, and other layers (including the plastic substrate film) other than the hardcoat.
Antireflection properties may be imparted to the hardcoat film with the hardcoat of the present invention being applied thereon. This can be attained, for example, by further forming an anitreflection layer on the surface of the hardcoat. The antireflection layer may be formed on the surface of the hardcoat by the following methods {circle around (1)} to {circle around (6)}.
{circle around (1)} A method wherein an about 0.1 xcexcm-thick very thin layer of MgF2 or the like is formed as the antireflection layer.
{circle around (2)} A method wherein a metal layer is deposited as an antireflection layer.
{circle around (3)} A method wherein a low refractive layer of a material having a lower light refractive index (refractive index: not more than 1.46) than the hardcoat is provided as an antireflection layer.
{circle around (4)} A method wherein a high refractive layer is provided so as to contact the hardcoat, and a low refractive layer is provided on the high refractive layer. In this case, the high refractive layer and the low refractive layer constitute an antireflection layer. For example, an ultrafine particle layer of a metal oxide having a high refractive index may be unevenly distributed in the antireflection layer in its region in contact with the hardcoat.
{circle around (5)} A method wherein the layer construction in {circle around (4)} is repeatedly stacked to form an antireflection layer.
{circle around (6)} A method wherein an intermediate refractive layer, a high refractive layer, and a low refractive layer are provided to form an antireflection layer.
In the production of the hardcoat for a plastic substrate film according to the present invention, the presence of the inorganic filler in the hardcoat in a larger amount in the outermost surface thereof than the interior thereof to form independent networks of the organic component and the inorganic filler is indispensable for improving both the strength and the flexibility of the hardcoat.
In order to realize the above ideal distribution of the inorganic filler and to form the independent network, the coating, which has been coated either directly or through other layer on the plastic substrate film, may be dried to remove the solvent contained in the coating followed by aging at a temperature of 20 to 100xc2x0 C. for 5 sec to 5 min to grow the reticular structure of the inorganic filler within the organic filler (percolation). Next, the coating is cured, for example, by irradiation with an ionizing radiation to obtain the hardcoat of the present invention with an independent network being formed therein.
For the aging, the temperature and the holding time should be properly varied according to the viscosity and glass transition temperature of the organic component used, the thickness of the coating and the like. In any case, however, aging under the above conditions can provide favorable properties.
Preferred inorganic fillers usable in the present invention have a particle diameter of 0.01 to 0.3 xcexcm. An inorganic filler in the above particle diameter range does not inhibit the motion of the segment of polymer chains, is likely to independently form a network and, at the same time, is not detrimental to the transparency of the coating. When the particle diameter is less than 0.01 xcexcm, the formation of an independent network is disadvantageously difficult, while a particle diameter exceeding 0.3 xcexcm is unfavorably detrimental to the transparency.
Regarding the type of the inorganic filler, ultrafine particles of a metal oxide are preferred because they form a strong reticular network in the coating due to strong cohesive force derived from the large surface area. Ultrafine particles of metal oxides usable herein include ultrafine particles of silica, alumina, titania, zirconia, tin oxide, and ITO. The inorganic filler is dispersed in the matrix resin, and, when the content of the inorganic filler is in a given content range, the inorganic filler can reticularly cohere, leading to the formation of a reticular structure through percolation.
The inorganic filler used in the present invention is such that a polymerizable functional group has been introduced into at least a part of the inorganic filler described above. The amount of the polymerizable functional group in the inorganic filler is preferably 0.01 xcexcmol to 10 mmol per g of the inorganic filler. When the amount of the polymerizable functional group is less than the lower limit of the above amount range, the inorganic filler is not covalently bonded to the organic component. On the other hand, when the amount of the polymerizable functional group exceeds the upper limit of the above amount range, the network structure of the inorganic filler particles per se is broken. This causes inorganic filler particles to cohere, disadvantageously resulting in extremely lowered strength of the coating.
According to the present invention, the one or more organic components are preferably such that at least one of the organic components is an ionizing radiation curing resin material having 4 moles or more, per molecule, of a polymerizable functional group which, upon exposure, for example, to heat or ultraviolet light or an electron beam, is polymerized to form a three-dimensionally reticular network. In this case, if hydroxyl, carboxyl, amido and other hydrogen bond-forming groups are present in the organic component, the surface of the ultrafine particles of the metal oxide and the organic component are strongly bonded to each other through a hydrogen bond, resulting in breaking of the network structure of the particles per se. This is likely to create such a structure in the hardcoat that particles locally cohere. In this case, the formed hardcoat lacks in flexibility. For this reason, preferably, at least one of the one or more organic components does not have any hydrogen bond-forming group.
The molecular weight of the organic component used in the present invention is preferably 1000 to 30000 in terms of the number average molecular weight. When the molecular weight is less than 1000, a strong network cannot be formed. On the other hand, when the molecular weight is more than 30000, this excessively large molecular weight unfavorably inhibits the formation of the network of the inorganic filler.
Specific examples of preferred organic components having a polymerizable functional group and free from a hydrogen bond-forming group usable in the present invention include polyfunctional acrylates, such as dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, and urethane (meth)acrylate, epoxy (meth)acrylate, polyester acrylate, polyacryl acrylate, and other oligomers or polymers having 4 moles or more, per molecule, of a polymerizable functional group.
According to the present invention, the weight ratio of the organic component to the inorganic filler is preferably 2:8 to 7:3, particularly preferably 3:7 to 6:4. In the conventional hardcoat, the content of the inorganic filler therein is about 3:7 in terms of the ratio of the inorganic filler to the organic component. On the other hand, according to the present invention, use of one or more organic components, at least one of the organic components being free from a hydrogen bond-forming group and having a polymerizable functional group, have enabled the amount of the inorganic filler added to be increased to a value much larger than that used in the conventional hardcoat. Therefore, the hardness can be enhanced, and, at the same time, the formation of the network structure of the inorganic filler can be facilitated. When the amount of the inorganic filler is excessively large, the hardcoat becomes very brittle although the hardness of the coating is increased. On the other hand, when the amount of the organic component is excessively large, the hardness of the coating is extremely lowered.
The plastic substrate film, which is effective in the hardcoat film according to the present invention, has a pencil hardness of about 4B to HB. An example of this type of plastic substrate films is a polyethylene terephthalate film. In applying the hardcoat film onto an object, when the surface of the object in the assembly should be visible, the plastic substrate film should be transparent. The pencil hardness of the hardcoat per se is 2H to 5H.
According to the present invention, xe2x80x9cpencil hardness of the hardcoat per sexe2x80x9d is a pencil hardness as measured, by the pencil hardness test according to JIS K 5400, for a coat formed by coating of the material onto a not less than 100 xcexcm-thick polyethylene terephthalate film to a thickness of about 5 xcexcm on a dry basis. In the pencil hardness test, the test is repeated five times for each of pencils having different hardnesses to determine the hardness of the pencil which, in the repetition of the test five times, did not cause any abnormal phenomenon in the appearance, such as a scratch. For example, in the repetition of the test five times using a pencil of 3H, when any abnormal phenomenon did not occur in the appearance, the pencil hardness of the material is at least 3H.
According to the present invention, xe2x80x9cpencil hardness of the hardcoat filmxe2x80x9d refers to a pencil hardness, as measured by the pencil hardness test according to JIS K 5400, for hardcoat films comprising the hardcoat formed on various plastic substrate films, and is evaluated in the same manner as described above in connection with the xe2x80x9cpencil hardness of the hardcoat per se.xe2x80x9d In this connection, it should be noted that the pencil hardness of the hardcoat film is influenced by the material of the hardcoat, the thickness of the hardcoat, and other layers (including the plastic substrate film) other than the hardcoat.
Antireflection properties may be imparted to the hardcoat film with the hardcoat of the present invention being applied thereon. This can be attained, for example, by further forming an antireflection layer on the surface of the hardcoat. The antireflection layer may be formed on the surface of the hardcoat by the following methods {circle around (1)} to {circle around (6)}.
{circle around (1)} A method wherein an about 0.1 xcexcm-thick very thin layer of MgF2 or the like is formed as the antireflection layer.
{circle around (2)} A method wherein a metal layer is deposited as an antireflection layer.
{circle around (3)} A method wherein a low refractive layer of a material having a lower light refractive index (refractive index: not more than 1.46) than the hardcoat is provided as an antireflection layer.
{circle around (4)} A method wherein a high refractive layer is provided so as to contact the hardcoat, and a low refractive layer is provided on the high refractive layer. In this case, the high refractive layer and the low refractive layer constitute an antireflection layer. For example, an ultrafine particle layer of a metal oxide having a high refractive index may be unevenly distributed in the antireflection layer in its region in contact with the hardcoat.
{circle around (5)} A method wherein the layer construction in {circle around (4)} is repeatedly stacked to form an antireflection layer.
{circle around (6)} A method wherein an intermediate refractive layer, a high refractive layer, and a low refractive layer are provided to form an antireflection layer.
According to the process for forming the hardcoat of the present invention, the formation of independent networks of the organic component and the inorganic filler in the hardcoat is indispensable for improving both the strength and the flexibility of the hardcoat. In order to form the above independent networks, the coating, which has been coated onto the plastic substrate film, may be dried to remove the solvent contained in the coating followed by aging at a temperature of 25 to 100xc2x0 C. for 5 sec to 5 min to grow the reticular structure of the inorganic filler within the organic filler (percolation). Next, the coating is cured, for example, by irradiation with an ionizing radiation to obtain the hardcoat of the present invention with an independent network being formed therein.
For the aging, the temperature and the holding time should be properly varied according to the viscosity and glass transition temperature of the organic component used, the thickness of the coating and the like. In any case, however, aging under the above conditions can provide favorable properties.
Heat reflecting properties may be imparted to a hardcoat film with the hardcoat of the present invention applied thereonto. This can be attained, for example, by further forming a high refractive conductive layer of ITO, ATO or the like on the surface of the hardcoat.
Ultraviolet shielding properties may be imparted to a hardcoat film with the hardcoat of the present invention applied thereonto. This can be attained, for example, by further forming a thin layer of a material having high ultraviolet absorption capacity, such as titania or zinc oxide, on the surface of the hardcoat.